The present invention relates to an apparatus and method for reacting a gas stream with a liquid, and more particularly to an improved gas-liquid contactor and method of operating the same.
Natural gas can contain a number of non-hydrocarbon impurities both in the formation prior to extraction and/or following extraction at a wellhead. Some of these impurities are detrimental to efficient pipeline operation, whereas others have no effect on pipeline efficiency, but do affect the heat content or Btu rating of the natural gas.
Nearly all natural gas contains some water vapor when extracted. The water vapor content in natural gas can be much lower than saturation, but is usually higher than that desired for satisfactory pipeline operation. The formation of free water in pipelines caused by pressure and/or temperature reduction can result in the formation of hydrates. In addition to the problem of hydrates, the formation of free water or condensation can add to the power requirements involved in distributing gas through pipelines, due to increased pressure drops caused when water collects in low spots in the line and reduces the pipeline flow area for the gas. This condition is also conducive to corrosion in the pipe. Water vapor is therefore usually removed from the gas, and various methods are used for removal of these vapors.
Sour gas is the name commonly given to natural gas containing hydrogen sulphide H2S. H2S is found in natural gas in concentrations varying from a trace up to 30% by weight. The presence of H2S causes severe corrosion to occur when free water is present in natural-gas pipelines. When burned, H2S forms sulphur dioxide, which is very toxic. The presence of H2S in natural gas is therefore a serious problem. Mercaptans, when airborne, can also present a problem because they have a foul smell.
Nitrogen is also frequently found in natural gas. It has no detrimental effects other than to lower the heat content of the gas. Oxygen is sometimes encountered in natural gas, but the quantities are usually so low as to be negligible. Another impurity that is only rarely encountered is helium, and the removal of helium is a specialized low-temperature process.
The basic processes used for removal of hydrocarbons invariably result in the removal of water vapors and unwanted acid components. The removal of water vapor or the adjustment of dew points is normally achieved by means of a glycol system that requires a counter current flow tower and glycol recovery system. H2S is normally removed as a gas using Amine systems, again requiring the Amine to be regenerated, often by a heated system. Conventional systems and a new compact contactor are described in US Patent No PCT/US2005/0020038. Furthermore, U.S. Pat. No. 6,918,949 B1 describes a method of contacting large volumes of gas, and U.S. Pat. No. 4,279,743 describes an air-sparged hydrocyclone.
It is an object of the invention to provide an improved gas-liquid contactor or Rapid Mass Transfer unit (RMT).